The intestinal absorption of cholesterol and other lipids is being studied in vitro using a special incubation system designed to permit the assessment of some of the factors which control or influence the initial phases of uptake across the mucosal cell membrane and the fluid layer overlying the membrane. Factors to be examined include the thickness of the fluid layer, the size of the bile salt micelles in which cholesterol and other lipids are dispersed, the concentration of the micelles, the effects of phosphatidylcholine and the effects of certain plant sterols structurally related to cholesterol. The purpose of the study is to extend our understanding of these processes with the view to providing a more rational basis for 1) preventing or suppressing absorption of cholesterol and other lipids in certain clinical entities associated with excessive intake, absorption or excessive blood levels such as obesity and hypercholesterolemia or 2) enhancing their absorption in cases where this is desirable such as malabsorption syndromes and malnutrition.